Method of producing solar cell

ABSTRACT

A method of producing a solar cell, including: a first coating step in which a pre-wet composition is spin-coated on a surface of a semiconductor substrate; a second coating step in which a diffusing material including a solvent and a diffusing agent containing a first impurity element is spin-coated on the surface where the pre-wet composition has been spin-coated, so as to form a coating film of the diffusing agent; and a first impurity diffusion layer forming step in which the semiconductor substrate having the coating film formed thereon is heated, so as to form a first impurity diffusion layer in which the impurity element contained in the diffusing agent is diffused.

FIELD OF THE INVENTION

The present invention relates to a method of producing a solar cell.

Priority is claimed on Japanese Patent Application No. 2013-226685,filed Oct. 31, 2013, the content of which is incorporated herein byreference.

DESCRIPTION OF THE RELATED ART

In recent years, solar cell is attracting attention in variousapplications. In the production process of a solar cell, there is a stepin which a diffusing agent is applied to a surface of a semiconductorsubstrate. There have been demands for producing solar cells at lowcosts and short tact time (cycle time).

As a method of applying a diffusing agent, there is known a method inwhich a diffusing agent is applied by spin-coating (for example, seePatent Literature 1).

As a method of applying a liquid material by spin-coating method, in thefield of resist application, a technique in which a coating solutioncontaining a resist material is known. Spin-coating is a technique whichenables formation of a coating film with a uniform film thickness.Therefore, for example, spin-coating is employed in the step of resistapplication in a process of forming a semiconductor device by aphotolithography technology.

DOCUMENTS OF RELATED ART Patent Documents

-   [Patent Literature 1] Japanese Unexamined Patent Application, First    Publication No. 2012-30160

SUMMARY OF THE INVENTION

When a coating film is formed on a substrate by spin-coating, most ofthe coating solution supplied onto the substrate is scattered outwardlyfrom the substrate by a centrifugal force, and a coating film is formedby the coating solution remaining on the substrate.

Thus, a large portion of the coating solution used would be wasted.

In the formation of a solar cell, when a diffusing agent is applied byspin-coating in the manner as described in Patent Literature 1, a largeamount of the expensive diffusing agent would be wasted. Further, inorder to produce a solar cell at a low cost by using spin-coating, ifthe amount of diffusing agent is merely reduced, the coating solutionwould not spread to the edge of the substrate, such that the coatingfilm is not formed at some portions. Further, formation defect of thecoating film is likely to occur, such as formation of voids in thecoating film. Therefore, in order to uniformly apply a diffusing agent,it becomes necessary to use a large amount of the diffusing agent,thereby resulting in difficulty to meet the demands to produce a solarcell at a “low cost”.

On the other hand, in the field of resist application, when a coatingfilm is formed on a substrate by spin-coating, the rotation time of thesubstrate is set to be long (for example, about 30 seconds to about 1minute), so as to even the film thickness of the coating film. In theformation of a solar cell, when a diffusing agent is applied byspin-coating in the manner as described in Patent Literature 1, if therotation time of the substrate is shortened in order to shorten the tacttime, uneven coating is likely to occur, and it becomes difficult toform a uniform coating film. Therefore, it was difficult to meet thedemands for producing a solar cell with “a short tact time”.

The present invention takes the above circumstances into consideration,with an object of providing a method of producing a solar cell which maysuppress the amount of the diffusing agent used, and also suppressformation defect of the coating film of the diffusing agent whileshortening the tact time.

A method of producing a solar cell according to one aspect of thepresent invention includes: a first coating step in which a pre-wetcomposition is spin-coated on one face of a semiconductor substrate;

a second coating step in which a diffusing material including a solventand a diffusing agent containing a first impurity element is spin-coatedon the one face where the pre-wet composition has been spin-coated, soas to form a coating film of the diffusing agent; and a first impuritydiffusion layer forming step in which the semiconductor substrate havingthe coating film formed thereon is heated, so as to form a firstimpurity diffusion layer in which the first impurity element containedin the diffusing agent is diffused.

According to the above method, the diffusing material can be spin-coatedin a state where the substrate surface is wetted with the pre-wetcomposition. As a result, the diffusing material can be reliablywet-spread in a short time.

Further, since the diffusing material is wet-spread over the entire faceof one face of the substrate while compatibilizing with the pre-wetcomposition, even if the amount of the diffusing agent used is small,the diffusing material can be effectively wet-spread over entire face ofone face of the substrate, so as to easily form a coating film of thecoating agent on the entire face of the one face of the substrate.

Thus, there can be provided a method of producing a solar cell which maysuppress the amount of the diffusing agent used, and also suppressformation defect of the coating film of the diffusing agent whileshortening the tact time.

In one embodiment according to the present invention, the method mayinclude, prior to the first coating step, a step in which a texturedstructure (concave/convex structure) is formed on at least the one faceof the substrate.

According to the above method, the one face having the texturedstructure formed is capable of more reliably holding the pre-wetcomposition, and the entire face of the one face becomes capable of morereliably maintaining a wet state with the pre-wet composition in theform of a film. As a result, spin-coating of the diffusing materialbecomes easier.

In one embodiment according to the present invention, the method mayinclude, in the second coating step, forming the coating film in asemi-dried state.

According to the above method, the tact time can be shortened, ascompared to the case where the rotation of the substrate is stoppedafter entirely drying the coating film. Further, since the rotation timeof the substrate is shortened, the coating film is unlikely to beadversely affected by wind shear.

In one embodiment according to the present invention, the method mayinclude, from the start of the first coating step to the end of thesecond coating step, continuously conducting spin-coating withoutstopping rotating the semiconductor substrate.

According to the above method, a centrifugal force is constantly appliedto the pre-wet composition and the diffusing material applied to the oneface. As a result, the pre-wet composition and the diffusing materialare scattered around the substrate without sneaking to the other face ofthe substrate, thereby suppressing contamination of the other face.

In one embodiment according to the present invention, in the method, themaximum substrate rotation number in the second coating step may belarger than the maximum substrate rotation number in the first coatingstep, and in the second coating step, after supplying the diffusingmaterial to the one face, the substrate rotation number in the firstcoating step may be increased to the substrate rotation number in thesecond coating step.

According to the above method, uneven coating of the diffusing materialis unlikely to occur.

In one embodiment according to the present invention, the method mayinclude, after the first impurity diffusion layer forming step, a secondimpurity diffusion layer forming step in which a second impuritydiffusion layer having a second impurity element diffused is formed onthe other face of the semiconductor substrate.

According to the above method, a high performance solar cell can beproduced.

According to the present invention, there can be provided a method ofproducing a solar cell which may suppress the amount of the diffusingagent used, and also suppress formation defect of the coating film ofthe diffusing agent while shortening the tact time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing an example of a solarcell substrate produced by the method of producing a solar cellaccording to the present embodiment.

FIG. 2 is a flow chart showing the method of producing a solar cellaccording to the present embodiment.

FIG. 3A is a process diagram showing the method of producing a solarcell according to the present embodiment.

FIG. 3B is a process diagram showing the method of producing a solarcell according to the present embodiment.

FIG. 3C is a process diagram showing the method of producing a solarcell according to the present embodiment.

FIG. 3D is a process diagram showing the method of producing a solarcell according to the present embodiment.

FIG. 3E is a process diagram showing the method of producing a solarcell according to the present embodiment.

FIG. 4A is a partially enlarged view showing the method of producing asolar cell according to the present embodiment.

FIG. 4B is a partially enlarged view showing the method of producing asolar cell according to the present embodiment.

FIG. 5 is a process diagram showing the method of producing a solar cellaccording to the present embodiment.

FIG. 6A is an explanatory diagram showing preferable conditions for thefirst coating step and the second coating step.

FIG. 6A is an explanatory diagram showing preferable conditions for thefirst coating step and the second coating step.

FIG. 7A is an explanatory diagram showing the defect caused in the casewhere pre-wetting is not conducted.

FIG. 7B is an explanatory diagram showing the defect caused in the casewhere pre-wetting is not conducted.

FIG. 7C is an explanatory diagram showing the defect caused in the casewhere pre-wetting is not conducted.

FIG. 8A is an explanatory diagram showing a substrate processingapparatus for working the method of producing a solar cell according tothe present embodiment.

FIG. 8B is an explanatory diagram showing a substrate processingapparatus for working the method of producing a solar cell according tothe present embodiment.

FIG. 9 is a block diagram showing an electric configuration of thesubstrate processing apparatus.

FIG. 10A is a diagram showing a main configuration of a coatingapparatus.

FIG. 10B is a diagram showing a main configuration of a coatingapparatus.

FIG. 11 is a diagram showing a main configuration of a nozzle part.

FIG. 12 is a flow chart showing a coating process of a diffusingmaterial by a coating apparatus.

FIG. 13A is an explanatory diagram showing a coating process by acoating apparatus.

FIG. 13B is an explanatory diagram showing a coating process by acoating apparatus.

FIG. 13C is an explanatory diagram showing a coating process by acoating apparatus.

FIG. 13D is an explanatory diagram showing a coating process by acoating apparatus.

FIG. 13E is an explanatory diagram showing a coating process by acoating apparatus.

FIG. 13F is an explanatory diagram showing a coating process by acoating apparatus.

FIG. 14 is a diagram showing a modified example of a substrateprocessing apparatus.

FIG. 15A is a graph showing the results of examples.

FIG. 15B is a graph showing the results of examples.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, one embodiment of the method of producing a solar cellaccording to the present invention will be described with reference tothe accompanying drawings. It should be noted that, in all drawings, formaking the drawings conspicuous, the size and proportion of eachcomponent are appropriately adjusted.

FIG. 1 is a schematic cross-sectional view showing an example of a solarcell substrate produced by the method of producing a solar cellaccording to the present embodiment.

The solar cell substrate 1000 includes an n-type silicon layer (nSilayer) 1001, a p⁺-type silicon layer (p⁺Si layer) 1002, an oxide film1003 and an n⁺-type silicon layer (n⁺Si layer) 1004.

The nSi layer 1001 is a layer of an n-type semiconductor, and isobtainable, for example, by diffusing an impurity element belonging togroup 15 of the periodic table into a monocrystalline silicon. Examplesof group 15 element include phosphorous (P), arsenic (As) and antimony(Sb). In the present embodiment, explanation will be given with respectto a case where P is contained as an impurity element. As the group 15element, 1 kind of element may be used, or 2 or more kinds of elementsmay be used in combination.

The p⁺Si layer 1002 is a layer of a p-type semiconductor, and isobtainable, for example, by diffusing an impurity element belonging togroup 13 of the periodic table into a monocrystalline silicon. Examplesof group 13 element include boron (B) and gallium (Ga). The impurityelement diffused in the p⁺Si layer 1002 corresponds to the “firstimpurity element” in the present invention. In the present embodiment,explanation will be given with respect to a case where B is contained asan impurity element. As the group 13 element, 1 kind of element may beused, or 2 or more kinds of elements may be used in combination.

The oxide film 1003 is an oxide film formed by the impurity elementcontained in the p⁺Si layer 1002, the silicon contained in themonocrystalline silicon substrate, and oxygen bonded together. In thepresent embodiment, explanation will be given with respect to a casewhere a borosilicate glass is formed as the oxide film.

The n⁺Si layer 1004 is a layer of an n-type semiconductor, and isobtainable, for example, by diffusing an impurity element belonging togroup 15 of the periodic table into a monocrystalline silicon. Further,the n⁺Si layer 1004 has higher impurity element concentration than thenSi layer 1001. The impurity element diffused in the n⁺Si layer 1004corresponds to the “second impurity element” in the present invention.Examples of the group 15 element are the same as defined for thoseusable for the nSi layer 1001. In the present embodiment, explanationwill be given with respect to a case where P is contained as an impurityelement. As the group 15 element, 1 kind of element may be used, or 2 ormore kinds of elements may be used in combination.

In the solar cell substrate 1000 shown in FIG. 1, after removing theoxide film 1003, the surface is subjected to a passivation treatment,followed by imparting electrodes to the front and rear surfaces, therebyconstituting a solar cell.

FIG. 2 is a flow chart showing the method of producing a solar cellaccording to the present embodiment. As shown in FIG. 2, the method ofproducing a solar cell according to the present embodiment includes thesteps of forming a textured structure on the substrate surface (texturedstructure forming step; step S11), pre-wetting of the substrate surface(first coating film forming step; step S121 of step S12), applying adiffusing material (second coating film forming step; step S122 of stepS12), forming a p⁺ layer (first impurity diffusion layer forming step;step S13) and forming an n⁺ layer (second impurity diffusion layerforming step; step S14).

Step S121 and step S122 are part of the step of forming a coating filmof the diffusing agent (step S12).

FIG. 3A to FIG. 3E, FIG. 4A, FIG. 4B and FIG. 5 are explanatory diagramsshowing the method of producing a solar cell according to the presentembodiment. FIG. 3A to FIG. 3E and FIG. 5 are process diagrams, and FIG.4A and FIG. 4B are partially enlarged views of FIG. 3C and FIG. 3D,respectively.

Hereinbelow, the method of producing a solar cell will be explained withreference to FIG. 2 to FIG. 5.

(Textured Structure Formation Step)

As shown in FIG. 3A, substrate W used in the method of producing a solarcell according to the present embodiment is a wafer WA having a circularshape in the plane view, in which part of the arc of the wafer WA iscut, so as to have a rectangular shape with rounded corners.

Such processing of the substrate W may be part of the production processof the solar cell. Alternatively, the production process of the solarcell may be conducted using a substrate W which has already beenprocessed to have a rectangular shape.

As the wafer WA, for example, a cylindrical ingot of a mono crystallinesilicon or the like produced by the CZ process (Czochralski process),the FZ process (Floating Zone process) or the like which is thinly cutin the direction perpendicular to the axial direction of the cylindermay be used. Further, in order to render the wafer WA an n-typesemiconductor, a group 15 impurity element is diffused entirely in thewafer WA in advance.

In general, as a solar cell, a solar cell unit is produced from a solarcell substrate, a plurality of solar cell units are connected to producea solar cell module, and a plurality of solar cell modules are connectedand arranged to obtain an array structure. Typically, a solar cellmodule is rectangular. Therefore, the wafer WA is processed to arectangular substrate W with rounded corners, so as to improve theefficiency of installing the substrate W in a module. The obtainedsubstrate W does not have a constant distance from the center portion WCof the substrate W to the outer periphery of the substrate W, and has adifference from the shortest distance L1 to the longest distance L2.

In the method of forming a solar cell according to the presentembodiment, firstly, as shown in FIG. 3B, one face Wa of the substrate Wis entirely subjected to an etching treatment with an alkali solutionAS, so as to form a textured surface (step S11 in FIG. 2). When the faceWa of the substrate W made of a monocrystalline silicon is subjected toetching with the alkali solution AS, due to the difference in thesolubility depending on the crystal orientation, anisotropic etching isapplied in line with the crystal orientation, and a textured structure(concave-convex structure) is formed over the entire face Wa. Etching isconducted, for example, until the height of the textured structurebecomes about 0.3 μm to 20 μm.

In a solar cell provided with such textured structure on the lightreceiving face, for example, as compared to a solar cell in which a facesubjected to a mirror finishing (such as a wafer for a semiconductordevice) is used as a light receiving face, light is reflected orrefracted on the textured structure, so as to be more reliably directedinto the substrate. As a result, the utilization efficiency of solarlight becomes high, thereby enabling a solar cell with high generationefficiency.

(First Coating Step)

Subsequently, as shown in FIG. 3C, a pre-wet composition 210 is suppliedfrom a nozzle 26 to one face Wa of the substrate W, followed byspin-coating, thereby forming a film of the pre-wet composition 210 overthe entire face Wa (step S121 in FIG. 2). The detailed coatingconditions are described later.

In the present embodiment, such forming of a film of a pre-wetcomposition of a surface of the substrate W is sometimes referred to as“pre-wetting”.

As the pre-wet composition, it is preferable to use an organic solvent.Examples of organic solvent include a monohydric alcohol, such asmethanol, ethanol, propanol or butanol; an alkylcarboxylic acid ester,such as methyl-3-methoxy propionate or ethyl-3-ethoxy propionate; apolyhydric alcohol, such as ethylene glycol, diethylene glycol orpropylene glycol; a polyhydric alcohol derivative, such as ethyleneglycol monomethyl ether, ethylene glycol monoethyl ether, ethyleneglycol monopropyl ether, ethylene glycol monobutyl ether, propyleneglycol monomethyl ether, propylene glycol monoethyl ether, propyleneglycol monopropyl ether, propylene glycol monobutyl ether,3-methoxy-3-methyl-1-butanol, 3-methoxy-1-butanol, ethylene glycolmonomethyl ether acetate, ethylene glycol monoethyl ether acetate,propylene glycol monomethyl ether acetate; a fatty acid, such as aceticacid or propionic acid; ketone, such as acetone, methyl ethyl ketone or2-heptanone.

Among these examples, in the present embodiment, it is preferable to usea protic polar solvent, such as the aforementioned monohydric alcohol,polyhydric alcohol, and polyhydric alcohol derivative, such as ethyleneglycol monomethyl ether, ethylene glycol monoethyl ether, ethyleneglycol monopropyl ether, ethylene glycol monobutyl ether, propyleneglycol monomethyl ether, propylene glycol monoethyl ether, propyleneglycol monopropyl ether, propylene glycol monobutyl ether,3-methoxy-3-methyl-1-butanol, and 3-methoxy-1-butanol.

As the pre-wet composition, one kind of organic solvent may be used, ora combination of organic solvents may be used. Further, the pre-wetcomposition may be mixed with water.

The organic solvent used as the pre-wet composition preferably has aboiling point of 30 to 200° C. Further, water to be used is preferably adeionized water (DIW).

The pre-wet composition 210 is preferably a mixed solvent of a proticpolar solvent and water. As the protic polar solvent, a monohydricalcohol or a polyhydric alcohol derivative is preferable. Since a highlywater-soluble organic solvent is advantageous in preparing a mixedsolvent, methanol, ethanol, propanol or butanol is preferable as themonohydric alcohol, and ethylene glycol monomethyl ether, ethyleneglycol monoethyl ether or propylene glycol monomethyl ether ispreferable as the polyhydric alcohol.

As a specific example of the pre-wet composition 210, a 1:1 mixedsolvent of propylene glycol monomethyl ether (PGME) and pure water maybe mentioned. The mixed solvent of PGME:DIW=1:1 is preferable ascompared to a mixed solvent with increased amount of PGME (e.g., a mixedsolvent of PGME:DIW=2:1) in that the diffusing agent described later canbe more reliably dissolved and a coating film of the diffusing agent canbe more reliably formed. Further, as compared to a mixed solvent with areduced amount of PGME (PGME:DIW=1:2), the mixed solvent of PGME:DIW=1:1is preferable in that the mixed solvent can be more reliably spread onthe surface of the substrate W during the spin-coating.

In the present embodiment, explanation will be given with respect to acase where a mixed solvent of PGME:DIW=1:1 is used as the pre-wetcomposition 210.

(Second Coating Step)

Subsequently, as shown in FIG. 3D, to the face Wa of the substrate W, adiffusing material 200 containing a diffusing agent is supplied from thenozzle 23, followed by spin-coating, thereby forming a coating film ofthe diffusing agent over the entire face Wa (step S122 in FIG. 2). Thedetailed coating conditions are described later.

The diffusing material 200 is a liquid material including a solvent anda diffusing agent containing an impurity element. Examples of theimpurity element include the aforementioned group 13 element and thegroup 15 element. Other examples of the impurity element include zincand copper.

As the diffusing agent contained in the diffusing material 200, anoxide, a halide, an inorganic salt such as a nitrate or a sulfate, anorganic acid salt such as an acetate, or an organic compound, each ofwhich containing an impurity element, may be used.

Specific examples of the diffusing agent include a boron compound, suchas B₂O₃, (RO)₃B, RB(OH)₂ or R₂B(OH); a gallium compound, such as(RO)₃Ga, RGa(OH), RGa(OH)₂ or R₂Ga[OC(CH₃)═CH—CO—(CH₃)]; a phosphorcompound, such as P₂O₅, NH₄H₂.PO₄, (RO)₃P, (RO)₂P(OH), (RO)₃PO,(RO)₂P₂O₃(OH)₃ or (RO)P(OH)₂; an arsenic compound, such as H₃AsO₃,H₂AsO₄, (RO)₃As, (RO)₅As, (RO)₂As(OH), R₃AsO or RAs═AsR; an antimonycompound, such as H₃SbO₄, (RO)₃Sb, SbX₃, SbOX or Sb₄O₅X; and a zinccompound, such as Zn(OR)₂, ZnX₂ or Zn(NO₂)₂. In the above formulae, Rrepresents a halogen atom, an alkyl group, an alkenyl group or an arylgroup, and X represents a halogen atom. Among these compounds, boronoxide (B₂O₃) or phosphorous oxide (P₂O₅) may be preferably used.

In the present embodiment, explanation will be given with respect to acase where boron oxide is used as the diffusing agent.

As the solvent contained in the diffusing material 200, the samesolvents as those described above for the pre-wet composition 210 may beused. As the solvent contained in the diffusing material 200, it ispreferable to use the same solvent as that used as the pre-wetcomposition 210. In the present embodiment, explanation will be givenwith respect to a case where a mixed solvent of PGME:DIW=1:1 is used asthe solvent contained in the diffusing agent 200.

Further, for forming a dielectric film, a leveling film or a protectivefilm simultaneously with diffusion of the diffusing material 200, thediffusing material 200 may contain a hydrolysis/polycondensation productobtainable from at least one alkoxysilane represented by the formula: R¹_(n)Si(OR²)_(4-n) as a starting material. In the formula, R¹ representsa hydrogen atom or a monovalent organic group, R² represents amonovalent organic group, and n represents an integer of 1 to 3.

Examples of the monovalent organic group for the alkoxysilane include analkyl group, an aryl group, an allyl group and a glycidyl group. Amongthese examples, an alkyl group and an aryl group is preferable.

The alkyl group preferably has 1 to 5 carbon atoms. Examples of thealkyl group include a methyl group, an ethyl group, a propyl group and abutyl group. The alkyl group may be straight-chained or branch-chained,and a hydrogen atom may be substituted with fluorine. The aryl grouppreferably has 6 to 20 carbon atoms. Examples of the aryl group includea phenyl group and a naphthyl group.

Specific examples of the alkoxysilane represented by the formula R¹_(n)Si(OR²)_(4-n) in which n=1 to 3, are as follows.

(i) In the case where n=1, an alkyl trialkoxysilane, such as methyltrimethoxysilane, methyl triethoxysilane, methyl tripropoxysilane, ethyltrimethoxysilane, ethyl triethoxysilane, ethyl tripropoxysilane, propyltrimethoxysilane or propyl triethoxysilane; a phenyl trialkoxysilane,such as phenyl trimethoxysilane or phenyl triethoxysilane.

(ii) In the case where n=2, a dialkyl dialkoxysilane, such as dimethyldimethoxysilane, dimethyl diethoxysilane, dimethyl dipropoxysilane,diethyl dimethoxysilane, diethyl diethoxysilane, diethyldipropoxysilane, dipropyl dimethoxysilane or dipropyl diethoxysilane;and a diphenyl dialkoxysilane, such as diphenyl dimethoxysilane ordiphenyldiethoxysilane.

(iii) In the case where n=3, a trialkylalkoxysilane, such as trimethylmethoxysilane, trimethyl ethoxysilane, trimethyl propoxysilane, triethylmethoxysilane, triethyl ethoxysilane, triethyl propoxysilane, tripropylmethoxysilane or tripropyl ethoxysilane; and a triphenyl alkoxysilane,such as triphenyl methoxysilane or triphenyl ethoxysilane.

Among these examples, a methyl trialkoxysilane, such as methyltrimethoxysilane, methyl triethoxysilane or methyl tripropoxysilane maybe preferably used.

The viscosity of the diffusing material 200 is preferably 0.7 mPa·s to50 mPa·s (0.7 cP to 50 cP). When the viscosity is from 0.7 mPa·s to 50mPa·s, uneven coating is unlikely to occur, and a coating film with asatisfactory film thickness can be reliably obtained. Further, itbecomes possible to spread the diffusing material 200 over the face Waunder the conditions where the substrate rotation speed is reducedduring spin-coating, such that splashed diffusing material 200 isunlikely to get adhered to the other face of the substrate W.

By spin-coating such diffusing material 200 and continuing rotation ofthe substrate W, the solvent contained in the diffusing material 200 isvolatilized, and a coating film of the diffusing agent is formed overthe entire face Wa. The film thickness of the coating film of thediffusing agent obtained after drying is preferably from 3,000 Å to10,000 Å.

The pre-wetting shown in FIG. 3C and FIG. 3D, and the formation of thecoating film of the diffusing agent will be described with reference toFIG. 4A and FIG. 4B. FIG. 4A is a partially enlarged view correspondingto FIG. 3C, and FIG. 4B is a partially enlarged view corresponding toFIG. 3D.

Firstly, as shown in FIG. 4A, when the pre-wet composition 210 isspin-coated on the face Wa, the pre-wet composition 210 is wet-spread asfar as the edge of the substrate W while being retained in the grooveportion (drain portion) DR of the textured structure T. That is, theface Wa having the textured structure formed is capable of more reliablyholding the pre-wet composition 210 than in the case of amirror-finished surface, and the entire face of the face Wa becomescapable of more reliably maintaining a wet state with the pre-wetcomposition 210 in the form of a film.

Subsequently, as shown in FIG. 4B, diffusing material 200 is supplied tothe face Wa, followed by spin-coating. In FIG. 4B, the state where thediffusing material 200 is wet-spread is indicated by the white arrow.

Generally, in the case where a liquid material is spin-coated on asurface of a substrate having a textured structure, the liquid materialmoving on the substrate surface is impeded by the textured structure.Therefore, it is difficult to wet-spread the liquid material as comparedto the case where the liquid material is spin-coated on a substratehaving a mirror-finished surface.

However, in the present embodiment, a film of the pre-wet composition210 is formed on the face Wa by pre-wetting, and by virtue of thepre-wet composition 210 being retained in the groove portion DR, thetextured structure is relieved. Therefore, when the diffusing material200 is spin-coated, the diffusing material 200 can be reliablywet-spread in a short time, as compared to the case where pre-wetting isnot conducted.

Further, the diffusing material 200 is spread as far as the edge of thesubstrate W by the centrifugal force of spin-coating whilecompatibilizing with the film of the pre-wet composition 210 formed onthe dace Wa. FIG. 4B shows the state of the diffusing material 200dissolving in the pre-wet composition 210 by black arrows.

In the method of producing a solar cell according to the presentembodiment, by virtue of the textured structure T being formed on theface Wa, the pre-wet composition 210 is satisfactorily held at thegroove portion DR, and the diffusing material 200 can be spread as faras the edge of the substrate W while dissolving the diffusing material200 in the pre-wet composition 210. Since the film of the pre-wetcomposition 210 is formed over the entire face Wa, the diffusingmaterial 200 can be spread over the entire face Wa by the above method,such that a coating film of the diffusing agent can be reliably formedover the entire face Wa.

Furthermore, even if the amount of diffusing material 200 supplied issmall, such that the amount of the diffusing agent used is small, thediffusing agent 200 can be efficiently wet-spread over the entire faceWa, and a coating film of the diffusing agent can be reliably formed onthe entire face Wa.

Moreover, as described above, since the diffusing material 200 iswet-spread while being compatibilized with the film of the pre-wetcomposition 210, in the production method according to the presentembodiment, the diffusing material 200 applied exhibits a viscositylower than the viscosity at the time of being supplied to the face Wa.For example, in the case where a diffusing material with a low viscosityis prepared, and spin-coating is conducted, the diffusing materialsneaks to the face of the substrate on the other side (the face oppositeto the face Wa), and likely to contaminate the other face. However, asin the production method according to the present embodiment, by virtueof spin-coating while reducing the viscosity of the supplied diffusingmaterial 200, the other face is unlikely to be contaminated, and hence,the step of cleaning the other face can be omitted.

(First Impurity Diffusion Layer Forming Step)

Subsequently, as shown in FIG. 3E, the substrate W having a coating filmof the diffusing agent is heated, so as to diffuse the impurity elementon the substrate, thereby forming an impurity diffusion layer on thesurface of the substrate (step S13 of FIG. 2).

Specifically, the diffusing agent is decomposed by the heat treatment,and the generated impurity element is thermally diffused to from thesurface of the substrate W made of monocrystalline silicon, therebyforming an impurity diffusion layer on the surface of the substrate W.In the present embodiment, since boron oxide is used as the diffusingagent, a p⁺-type Si layer 1002 which is a p⁺ layer is formed as animpurity diffusion layer. In FIG. 3E, in the substrate W, the portionother than the p⁺Si layer 1002 is indicated as the nSi layer 1001.

Further, on the surface of the substrate, boron contained in thediffusing agent, silicon contained in the substrate W and oxygen in airare reacted, so as to form an oxide film 1003 made of borosilicateglass.

(Second Impurity Diffusion Layer Forming Step)

Subsequently, as shown in FIG. 5, a second impurity element is diffusedon the other face of the substrate (opposite face of the face Wa), so asto form an impurity diffusion layer (step S14 in FIG. 2).

For example, as shown in FIG. 5, the substrate having the p⁺Si layer1002 and the oxide film 1003 formed is disposed inside a chamber C, agas containing a group 15 element is introduced into the chamber C, andthe inside of the chamber C is heated, thereby forming an impuritydiffusion layer. In the present embodiment, as the gas containing agroup 15 element, POCl₃ is used, so as to form a n⁺Si layer 1004 as then⁺-type layer.

Further, in the same manner as in the formation of the p⁺Si layer 1002,after forming a coating layer of the diffusing agent containing a group15 element on the other face, heat treatment may be conducted.

In the present embodiment, in such a manner, a solar cell substrate 1000usable in the production of a solar cell is produced.

In the following steps, suitable components are imparted, for example,on the surface of the solar cell substrate 1000 corresponding to theaforementioned one face, an anti-reflection film may be imparted, and onthe other surface of the solar cell substrate 1000 corresponding to theaforementioned other face, and electrodes are provided on both surfaces,thereby producing a solar cell.

FIG. 6A and FIG. 6B are explanatory diagrams showing preferableconditions for the first coating step and the second coating step.

FIG. 6A is an explanatory diagram showing conditions for spin-coating inthe first coating step and the second coating step. In FIG. 6A, thehorizontal axis indicates the rotation time (unit:seconds) of thesubstrate W during spin-coating, and the vertical axis indicates therotation speed (unit: rpm) of the substrate W during spin-coating.

As shown in FIG. 6A, in the first coating step, the substrate at astationary state is rotated up to a rotation speed R1 by the time T1.After reaching the predetermined rotation speed R1, the pre-wetcomposition 210 is applied to the face Wa of the substrate W, andspin-coating is conducted while maintaining the rotation speed at R1from the time T1 until the time T2.

Thereafter, in the second coating step, while maintaining the rotationspeed of the substrate W at R1, the diffusing material 200 is applied tothe face Wa, and spin-coating is conducted while maintaining therotation speed at R1 from the time T2 until the time T3.

Subsequently, from the time T3 to the time T4, the rotation speed of thesubstrate W is accelerated from R1 to R2, and spin-coating is conductedwhile maintaining the rotation speed at R2 from the time T4 until thetime T5.

Subsequently, from the time T5 to the time T6, the rotation speed of thesubstrate W is reduced from R2 to 0 rpm, and the second coating step isfinished.

The rotation time of the substrate from the start to T1 may beappropriately selected, considering the tact time. For example, therotation time from the start to T1 is 0.01 to 0.2 seconds.

The rotation time from T1 to T2 is, for example, 0.5 to 5 seconds. Inthe production method according to the present embodiment, the rotationtime from T1 to T2 is 5 seconds.

The rotation time from T2 to T3 is, for example, 0.5 to 1 second. In theproduction method according to the present embodiment, the rotation timefrom T2 to T3 is 1 second.

The rotation time from T3 to T4 is, for example, 0.1 to 1 second.

The rotation time from T4 to T5 is, for example, 3 to 8 second. In theproduction method according to the present embodiment, the rotation timefrom T4 to T5 is 5 seconds.

The rotation time from T5 to T6 is, for example, 0.1 to 1 second.

Further, with respect to the rotation time, R1 is 800 rpm to 3,000 rpm,and R2 is 1,000 rpm to 5,000 rpm. R1 is the maximum rotation speed ofthe substrate in the first coating step, and R2 is the maximum rotationspeed of the substrate in the second coating step. In the productionmethod according to the present embodiment, R1 is 800 rpm, and R2 is3,000 rpm.

In the spin-coating conditions shown in FIG. 6A, the spin-coating in thefirst coating step and the second coating is step is conductedcontinuously without stopping the rotation of the substrate W from thestart of the first coating step to the end of the second coating step.If the rotation of the substrate W is stopped between the first coatingstep and the second coating step, as shown in FIG. 6B, the pre-wetcomposition 210 spin-coated in the first coating step sneaks to theother face of the substrate W (opposite face of the face Wa) byself-weight, so as to contaminate the other face. However, if thesubstrate W is continuously rotated between the first coating step andthe second coating step, a centrifugal force is constantly applied tothe pre-wet composition 210. As a result, the pre-wet composition 210 isscattered around the substrate without sneaking to the other face of thesubstrate, thereby suppressing contamination of the other face.

Further, by continuously rotating the substrate W without stopping fromthe start of the first coating step to the end of the second coatingstep, other problems may be solved.

The substrate used in the production method according to the presentembodiment, as shown in FIG. 3A, does not have a constant distance fromthe central portion WC of the substrate W to the outer periphery of thesubstrate W. When such a substrate which does not have a constantdistance from the central portion WC to the outer periphery of thesubstrate W is rotated, the substrate is rotated while the edge of thesubstrate W, in particular, the straight line portion formed by cuttingthe substrate hits the surrounding air. Therefore, the surrounding airis moved, and an air stream is likely to be generated. Hereafter, suchphenomenon is referred to as “wind shear”.

When air is vigorously moved by wind shear, droplets of the diffusingmaterial 200 and the pre-wet composition 210 scattered by spin-coatingare carried by the flow of air and reach the other face of the substrateW, thereby contaminating the other face. The wind shear due to the shapeof the substrate W inevitably occurs. Therefore, in the productionmethod according to the present invention, operation conditions capableof reducing the influence of the wind shear during spin-coating as muchas possible is necessary.

From the view point of the above, the total of the rotation time of thesubstrate is preferably shorter in that spin-coating can be finishedbefore air is moved too much by the wind shear. Further, the change inthe rotation speed of the substrate is preferably smaller in thatmovement of air is unlikely to be disturbed by the wind shear.

As described above, by virtue of not stopping the rotation of thesubstrate W between the first coating step and the second coating step,the change in the rotation speed of the substrate can be reduced fromthe start of the first coating step to the end of the second coatingstep.

Furthermore, by setting the rotation time of the substrate in theabove-described time range, the tact time can be suppressed to about 15to 18 seconds, and contamination of the other face of the substrate W bythe wind shear can be suppressed.

Moreover, in the second coating step, it is preferable to control thetime from T4 to T5, so as to form a coating film of the diffusing agentin a semi-dried state. Here, a coating film of the diffusing agent is“in a semi-dried state” means that the fluidity of the diffusing agent200 is impaired, but the solvent is remaining such that natural dryingof the coating film can be visually observed when allowed to stand atroom temperature. For example in the case where rotation is continued atrotation speed R2 for 60 seconds to form a coating film, the coatingfilm will be satisfactorily dried, not semi-dried.

By stopping the rotation of the substrate when the coating film is in asemi-dried state, and the second coating step is finished, the tact timecan be shortened, as compared to the case where the rotation of thesubstrate is stopped after entirely drying the coating film. Further,since the rotation time of the substrate is shortened, the coating filmis unlikely to be adversely affected by wind shear.

Furthermore, as shown in the figure, in the second coating step, it ispreferable that, after supplying the diffusing material 200 to one face,the substrate rotation number in the first coating step is increased tothe substrate rotation number in the second coating step. In thismanner, uneven coating of the diffusing material 200 is unlikely tooccur.

In the production method according to the present invention, sincepre-wetting is conducted before forming a coating film of the diffusingagent on the face Wa of the substrate W, when the diffusing material 200containing the diffusing agent is spin-coated, the diffusing material200 is satisfactorily wet-spread on the face Wa. Therefore, the coatingfilm of the diffusing agent formed becomes an excellent coating filmwith no defects such as voids and uncoated parts. The effects of formingsuch a coating film will be explained below.

FIG. 7A to FIG. 7C are explanatory diagrams showing the defect caused inthe case where pre-wetting is not conducted. FIG. 7A and FIG. 7Bcorrespond to FIG. 3C and FIG. 3D, respectively, and FIG. 7C correspondsto FIG. 1.

In the case where the amount of the diffusing material 200 dripped isreduced in order to suppress the amount of the diffusing agent used, ifpre-wetting is not conducted, formation defects of the coating film suchas voids and uncoated parts are likely to occur. FIG. 7A shows the casewhere a diffusing material 200 is applied to a substrate W, and a void200 x is formed in the coating film of the diffusing material 200.

In the case where the coating state of the diffusing material 200 issuch that a void 200 x is formed as described above, when a firstimpurity diffusion layer is formed by heat treatment, the p⁺Si layer1002 is not formed at a position corresponding to the void 200 x.Further, at the position corresponding to the void 200 x, the oxide film1003 is not formed, and a void 1003 x is formed. On the bottom of thevoid 1003 x, the nSi layer 1001 (nSi layer 1001 x) remaining on thesurface of the substrate is exposed (FIG. 7B).

When such a substrate is used to form a second impurity diffusion layerwith a gas containing an impurity element in the manner as describedabove, the n⁺Si layer 1004 is formed on the other face of the substrate.Furthermore, the second impurity diffusion layer (n⁺Si layer 1004 x) isalso formed on the nSi layer 1001 exposed inside the void 1003 (FIG.7C). That is, a solar cell substrate 1000 x is obtained in a state wherethe p⁺Si layer 1002 and the n⁺Si layer 1004 x are mutually adjacent onthe same layer.

In the case where a solar cell is produced using such a solar cellsubstrate 1000 x, at the time of power generation, reverse current Irevis likely to be generated at a pn junction portion of the p⁺Si layer1002 and the n⁺Si layer 1004 x, and the solar cell is likely to sufferhot spot.

In the production of a solar cell, the entire substrate W used in theproduction becomes the actual solar cell product, and in the case wherea void 200 x is formed during the coating of the diffusing material 200,it is not possible to employ an operation to selectively discard thedefect portion around the void 200 x. Therefore, defects in theproduction of a solar cell as shown in FIG. 7A to FIG. 7C affect theentire solar cell.

In contrast, in the method of producing a solar cell according to thepresent embodiment, since the diffusing material 200 is spin-coatedafter pre-wetting is conducted using the pre-wet composition 210,formation defects of the coating film of the diffusing agent is unlikelyto be generated, and it becomes possible to produce a high-quality solarcell.

The method of producing a solar cell according to the present embodimentis as follows.

Herebelow, one example of an apparatus configuration capable of workingthe method of producing a solar cell according to the present embodimentwill be described.

FIG. 8A is an explanatory diagram showing a plan view of a substrateprocessing apparatus for working the method of producing a solar cellaccording to the present embodiment, and FIG. 8B is a cross-sectionalview taken along the A-A line in the arrow direction in FIG. 8A. FIG. 9is a block diagram showing an electric configuration of the substrateprocessing apparatus 100.

Hereinbelow, upon describing the configuration of the substrateprocessing apparatus 100, for the purpose of simple marking, an XYZcoordinate system is used to describe the directions in the drawings.The longitudinal direction of the substrate processing apparatus 100 andthe transporting direction of the substrate is marked as the Xdirection. The direction perpendicular to the X direction (substratetransporting direction) in the plan view is marked as the Y direction.The direction perpendicular to a plane including the X and Y axes ismarked as the Z direction. In the X, Y, and Z directions, the arrowdirection in the drawing is the +direction, and the opposite directionof the arrow direction is the −direction.

As shown in FIG. 8A and FIG. 8B, the substrate processing apparatus 100is equipped with a loading part 1 for loading a substrate W to betreated, a coating apparatus 10 provided on the downstream side (+Xdirection) of the loading part 1, a drying apparatus 3 provided on thedownstream side (+X direction) of the coating apparatus 10, a firsttransporting apparatus 6 which transports the substrate W from theloading part 1 to the drying apparatus 3, and a second transportingapparatus 7 which transports the substrate W in the drying apparatus 3.

As shown in FIG. 9, the substrate processing apparatus 100 is equippedwith a control part 9 which controls the actuation of each of theloading part 1, the coating apparatus 10, the drying apparatus 3, thefirst transporting apparatus 6 and the second transporting apparatus 7.

The drying apparatus 3 is constituted of 3 hot plates 3 a, 3 b and 3 cwhich are arranged in this order in toward the downstream side (+Xdirection). Each of the hot plates 3 a, 3 b and 3 c is divided intothree in the direction perpendicular to the substrate transportingdirection (Y direction), and each of the hot plates 3 a, 3 b and 3 c hasa gap 51 formed.

The second transporting apparatus 7 includes a thin-plate substratesupporting member 52 which is capable of advancing/retreating betweenthe back side and front side of the hot plates 3 a, 3 b and 3 c via thegap 51, a guide rod 53 which guides the substrate supporting member 52along the X direction, and a cylinder unit 54 which moves the substratesupporting member 52 along the X direction in line with the guide rod53. The drying apparatus 3 is electrically connected to the control part9, and actuation of each of the hot plates 3 a, 3 b and 3 c arecontrolled by the control part 9.

The coating apparatus 10 includes a chuck part 20 which holds thesubstrate W, a nozzle part 21 which drips a diffusing material to thesubstrate W held by the chuck part 20, and a cup part (anti-scatteringcup) 22 which accommodates the chuck part 20 rotating. The coatingapparatus 10 is the so-called spin-coater. The coating apparatus 10 iselectrically connected to control part 9, and the operation of the chuckpart 20 is controlled by the control part 9.

The first transporting part 6 includes a rail 60 provided along one side(−Y direction) of the substrate processing apparatus 100, a plurality ofmoving bodies 61 which moves along the rail 60, and a plurality ofsubstrate supporting members 62 which can be lifted up and down fromeach moving body 61 to an upper side (+Z direction) and support thesubstrate W. Each substrate supporting member 62 has a plurality ofsupporting claws 63 which support the substrate W. The firsttransporting apparatus 6 is electrically connected to the control part9, and actuations of the moving bodies 61 and the substrate supportingmembers 62 are controlled by the control part 9.

The first transporting apparatus 6 is capable of actuating the pluralityof moving bodies 61 independently. The moving bodies 61 are arranges atpositions where each moving body does not interfere with other movingparts when moved along the rail 60. By such configuration, for example,the first transporting apparatus 6 is capable of unloading the substrateW from the coating apparatus 10 after coating of the diffusing material200 by substrate supporting members 62 provided on one moving body 61and loading the substrate W into the drying apparatus 3, and at the sametiming, loading another substrate W from the loading part 1 into thecoating apparatus 10 by substrate supporting members 62 provided onanother moving body 61. In such a manner, the substrate processingapparatus 100 shortens the tact required for the coating step of thediffusing material 200 to the substrate W and the drying step.

The second transporting apparatus 7 is electrically connected to thecontrol part 9, and actuation of the cylinder unit 54 is controlled bythe control part 9. By conducting an extension operation of the cylinderunit 54 in the Z direction, the second transporting apparatus 7protrudes the upper end of the substrate supporting member 52 from thegap 51, so as to lift the substrate W on the hot plate 3 a. In thisstate, the substrate supporting member 52 is moved to the downstreamside together with the cylinder unit 54 along the guide rod 53. Then,the cylinder unit 54 is compressed, and the and the upper end of thesubstrate supporting member 52 is lowered below the upper face of thehot plate 3 a, so as to transfer the substrate W to the hot plate 3 b onthe downstream side. By repeating such operations, the substrate W canbe sequentially transferred to the hot plate 3 c on the downstream side.

FIG. 10A and FIG. 10B are diagrams showing a main configuration of thecoating apparatus 10. FIG. 10A shows a side-sectional view, and FIG. 10Bshows a plan view. In FIG. 10A and FIG. 10B, a state where the substrateW is disposed inside the coating apparatus 10 is shown.

As shown in FIG. 10A, the chuck part 20 is rotatable in a state wherethe substrate W is held by suction, and is capable of being lifted upand down relative to the cup part 22. Specifically, the chuck part 20 iscapable of being lifted up and down from a mounting position where thesubstrate W is mounted (substrate mounting position) to a rotatingposition where the rotation operation is conducted inside the cup part22 (rotating position).

The cup part 22 prevents the diffusing agent dripped on the substrate Wfrom being scattered around the substrate, and is equipped with a backface cleaning nozzle (cleaning nozzle) 22 a which cleans a back side ofthe substrate W. The back face cleaning nozzle 22 a is connected to acleaning liquid supply source (not shown). The cleaning liquid supplysource is configured to eject the cleaning liquid from the back facecleaning nozzle 22 a by pressurization.

As shown in FIG. 10B, the chuck part 20 according to the presentembodiment is circular in the plan view. On the other hand, since thesubstrate W held by the chuck part 20 is for use in a solar cell, thesubstrate W is square-shaped in the plan view, and has the four cornersrounded off.

The chuck part 20 has a diameter 40 to 70% of the length of the shortside of the substrate W. In the present embodiment, the diameter of thechuck part 20 is, for example, about ⅔ of the length of the short sideof the substrate W. Since the chuck part 20 has a diameter 40 to 70% ofthe length of the short side of the substrate W, and the four corners ofthe substrate W is rounded off, when the substrate W is likely to rattleduring rotation, the chuck part 20 is capable of satisfactorily holdingthe substrate W. Further, even in the case where a substrate W having asmall thickness is used, the chuck part 20 is capable of reliablyholding the substrate W.

Next, the configuration relationship of the chuck part 20 and the backface cleaning nozzle 22 a will be explained. As shown in FIG. 10B, theback face cleaning nozzle 22 a is disposed approximately middle betweenthe outer edge of the chuck 20 and the outer edge of the substrate W.According to the above configuration, the cleaning liquid can besupplied to the back face of the substrate W rotated by the chuck part20 at a position approximately concentric relative to the outer edge ofthe chuck part 20.

The coating apparatus 10 is capable of conducting the so-called backrise treatment in which an alcohol as a cleaning liquid is ejected fromthe back face cleaning nozzle 22 a to the back face of the substrate Wat the same timing as dripping the diffusing material on the surface ofthe substrate W. Examples of the alcohol as the cleaning liquid includealcohols having 1 to 5 carbon atoms, such as methanol, ethanol,propanol, butanol, 3-methoxy-3-methyl-1-butanol and 3-methoxy-1-butanol.

Specifically, in the present embodiment, the distance D of the back facecleaning nozzle 22 a from the outer edge of the short side of thesubstrate W held by the chuck part 20 is within 10 mm. By suchconfiguration, the cleaning liquid supplied from the back face cleaningnozzle 22 a to the back face of the substrate W is satisfactorily spreadto the outer edge of the substrate W, and by preventing the diffusingmaterial from sneaking to the back face of the substrate W, there is noneed to separately conduct a back rinse treatment after coating of thediffusing material, thereby shortening the tact of the coating step.

FIG. 11 is a diagram showing a main configuration of the nozzle part 21.

As shown in FIG. 11, the nozzle part 21 includes a first nozzle 23provided with an opening 23 a from which the diffusing material 200 isdripped, a second nozzle 26 provided with an opening 26 a from which thepre-wet composition 210 is dripped, and an accommodation part 24 whichaccommodates the first nozzle 23 and the second nozzle 26.

As shown in FIG. 11, the accommodation part 24 includes a lid part 24 aintegrally provided with the first nozzle 23 and the second nozzle 26,and a main body 24 b which forms a closed space that accommodates aportion of the first nozzle 23 and the second nozzle 26 (tip portion)together with the lid part 24 a. In such a manner, by accommodating thetip portions of the first nozzle 23 and the second nozzle 26 in a closedstate, the accommodation part 24 is capable of preventing the openings23 a and 26 a from getting dried. The lid part 24 a moves together withthe first nozzle 23 and the second nozzle 26, and the main body 24 bdoes not move from the standby position of the nozzle part 21.

In the present embodiment, the first nozzle 23 and the second nozzle 26are integrally held by the lid part (holding member) 24 a. The firstnozzle 23 is disposed such that the opening 23 a is arranged in thevertical direction (Z direction). That is, the first nozzle 23 is heldby the lid part 24 a such that the dripping direction of the droplets ofthe diffusing agent dripped from the opening 23 a is along the verticaldirection.

On the other hand, the second nozzle 26 is disposed such that the axiswhich runs through the center of the opening 26 a is inclined relativeto the vertical direction (Z direction). That is, the second nozzle 26is held by the lid part 24 a such that the dripping direction of thedroplets of the pre-wet composition dripped from the opening 26 a isinclined relative to the vertical direction.

The first nozzle 23 held by the lid part 24 a is capable of dripping thediffusing agent from an upper side of the substrate Win the verticaldirection. On the other hand, the second nozzle 26 is held by the lidpart 24 a such that, when the first nozzle 23 is disposed at a positionwhere the diffusing agent can be dripped to a central portion of thesubstrate W, the second nozzle 26 can drip the pre-wet composition fromdiagonally upper side of the central portion WC of the substrate W tothe central portion of the substrate W. That is, in the presentembodiment, the lid part 24 a constitutes a regulation means whichregulates the landing position of the droplets of the pre-wetcomposition such that the droplets are dripped on the central portion ofthe substrate W.

The fixing angle of the second nozzle 26 on the lid part 24 a, i.e., theinclination angle of the axis of the second nozzle 26 relative to thevertical direction may be appropriately selected depending on thepositional relation of the substrate W and the openings 23 a and 26 aand the sizes of the nozzles 23 and 26. For example, the angle ispreferably set in the range of 30 to 45°, and more preferably 45°. It isnot always necessary that the second nozzle 26 is entirely inclined, anda configuration in which only the tip portion is inclined at the aboveangle may be employed. By such configuration, the space for installingthe second nozzle 26 can be saved, and the size of the nozzle part 21can be reduced.

The nozzle part 21 includes a transfer mechanism (transfer part) 25which transfers the lid part 24 a. The transfer mechanism 25 is capableof integrally transferring (advancing/retreating) the first nozzle 23and the second nozzle 26 relative to the chuck part 20. By suchconfiguration, the first nozzle 23 and the second nozzle 26 are capableof being advanced/retreated in parallel to the loading direction of thesubstrate Won the chuck part 20. As a result, the transfer distance ofthe first nozzle 23 and the second nozzle 26 can be reduced, and thetact of the entire coating process can be shortened.

Further, inside the first nozzle 23, a flow path (not shown) whichallows the diffusing material 200 to flow to the opening 23 a isprovided, and the flow path is connected to a diffusing material supplysource (not shown).

The diffusing material supply source has, for example, a pump (notshown). By pushing out the diffusing material to the opening 23 a, thediffusing material 200 is dripped from the opening 23 a.

Further, inside the second nozzle 26, a flow path (not shown) whichallows the pre-wet composition 210 to flow to the opening 26 a isprovided, and the flow path is connected to a pre-wet composition supplysource (not shown). The pre-wet composition supply source has, forexample, a pump (not shown). By pushing out the pre-wet composition tothe opening 26 a, the pre-wet composition 210 is dripped from theopening 26 a.

Next, the operation of the substrate processing apparatus 100 will bedescribed, mainly with respect to the coating step of the diffusingmaterial on the substrate W by the coating apparatus 10.

FIG. 12 is a flow chart showing a coating process of a diffusingmaterial by the coating apparatus 10.

The coating step of the diffusing material by the coating apparatus 10includes a mounting step S1, a nozzle transfer step S2, a nozzlelift-down step S3, a pre-wet composition dripping step S4, a diffusingmaterial dripping step S5, a nozzle lift-up step S6 and a nozzlewithdrawing step S7.

The coating step performed by the coating apparatus 10 corresponds tostep S12 in FIG. 2.

The mounting step S1 is a step in which a substrate W is mounted on thechuck part 20 at a substrate mounting position.

The nozzle transfer step S2 is a step in which the nozzle part 21 istransferred to the upper side of the chuck part 20 at the substratemounting position.

The nozzle lift-down step S3 is a step in which the chuck part 20 havingthe substrate W mounted thereon is transferred from the substratemounting position to the rotating position where the rotating operationis conducted inside the cup part 22, and the nozzle part 21 is lifteddown.

The pre-wet composition dripping step S4 is a step in which the pre-wetcomposition 210 is dripped from the opening 26 a of the second nozzle 26to the substrate W on the chuck part 20 transferred to the rotatingposition, and the chuck part 20 is rotated.

The diffusing material dripping step S5 is a step in which the diffusingmaterial 200 is dripped from the opening 23 a of the first nozzle 23 tothe substrate W having the pre-wet composition 210 dripped thereon, andthe chuck part 20 is rotated.

The nozzle lift-up step S6 is a step in which the nozzle part 21 islifted up to withdraw the nozzle part 21 from the chuck part 20.

The nozzle withdrawing step S7 is a step in which the nozzle part 21 iswithdrawn from the inside of the cup part 22.

Hereinbelow, referring to FIG. 13A to FIG. 13F, the coating step will bedescribed.

Firstly, as shown in FIG. 13A, the substrate processing apparatus 100passes the substrate W loaded from the loading part 1 to the coatingapparatus 10 by the first transporting apparatus 6 (mounting step S1).At this time, the chuck part 20 is lifted up to the mounting positionwhere the substrate W transferred by the substrate supporting member 62is to be mounted. Further, in preparation of a subsequent coating step,the substrate processing apparatus 100 loads another substrate W insidethe loading part 1.

In the present embodiment, for example, at the same timing as mountingthe substrate W on the chuck part 20, the nozzle part 21 faces thesubstrate W (nozzle transfer step S2). Specifically, the nozzle part 21is transferred to a position where the opening 23 a of the first nozzle23 faces the central portion WC of the substrate W. Since the nozzlepart 21 faces the substrate W at the same timing as when the substrate Wis mounted on the chuck part 20 as described above, the waiting time oftransferring the nozzle part 21 to the chuck part 20 can be eliminated,and the tact can be shortened.

As shown in FIG. 13B, when the substrate W is mounted, the control part9 (see FIG. 9) actuates the chuck part 20 so as to suction and hold thesubstrate W, and controls the nozzle part 21 to be lifted down togetherwith the chuck part 20 (nozzle lift-down step S3). By lifting down thenozzle part 21 together with the chuck part 20, the distance between thesubstrate W and the openings 23 a and 26 a can be maintained at apredetermined value, each material can be satisfactorily dripped ontothe substrate W in the later dripping steps.

As shown in FIG. 13C, when the substrate W held by the chuck part 20reached the rotating position at which the substrate W is rotated insidethe cup part 22, the control part 9 (see FIG. 9) controls the chuck part20 to rotate. The control part 9 drips the pre-wet composition 210 fromthe opening 26 a of the second nozzle 26 to the substrate S whilerotating the chuck part 20 (pre-wet composition dripping step S4). Inthe present embodiment, the second nozzle 26 is held by the lid part 24a such that the pre-wet composition 210 can be dripped from a diagonallyupper side of the central portion WC of the substrate W to the centralportion WC of the substrate W. Therefore, the second nozzle 26 can allowthe droplets dripped from the opening 26 a to land on the centralportion WC of the substrate W.

After dripping a predetermined amount (e.g., 2.0 ml) of the pre-wetcomposition 210 from the second nozzle 26 onto the substrate W, thecontrol part 9 (see FIG. 9) rotates the chuck part 20 for apredetermined time.

In the present embodiment, in the pre-wet composition dripping step S4,for example, the chuck part 20 is rotated at a rotation number of 800rpm for 3 seconds. In this manner, the pre-wet composition 210 drippedon the central portion WC of the substrate W is wet-spread on the entiresubstrate W.

Subsequently, as shown in FIG. 13D, the control part 9 (see FIG. 9)drips the diffusing material 200 from the opening 23 a of the firstnozzle 23 to the substrate W while rotating the substrate W held by thechuck part 20 in the cup part 22 (diffusing material dripping step S5).In the present embodiment, the first nozzle 23 is held by the lid part24 a such that the diffusing material 200 can be dripped from the upperside of the central portion WC of the substrate W to the central portionWC of the substrate W. Therefore, the first nozzle 23 can allow thedroplets dripped from the opening 23 a to land on the central portion WCof the substrate W.

The control part 9 (see FIG. 9) rotates the chuck part 20 for apredetermined time while dripping the diffusing material 200 from thefirst nozzle 23 onto the substrate W. In the present embodiment, forexample, the chuck part 20 is rotated at a rotation number of 800 rpmfor 0.5 to 1.0 seconds. In this manner, the diffusing material 200 canbe wet-spread to the extent where the diffusing material 200 does notspread out of the surface of the substrate W.

After dripping a predetermined amount of the diffusing material 200 fromthe first nozzle 23 to the substrate W, as shown in FIG. 13E, thecontrol part 9 (see FIG. 9) controls the nozzle part 21 to be lift up(nozzle lift-up step S6). The control part 9 rotates the chuck part 20for a predetermined time while lifting up the nozzle part 21. In thepresent embodiment, for example, the chuck part 20 is rotated at arotation number of 2,000 rpm within 5 seconds.

In this manner, the diffusing agent 200 dripped on the central portionWC of the substrate W is wet-spread on the entire substrate W. In thismanner, the diffusing material 200 can be shaken off the surface of thesubstrate W.

In the present embodiment, since the first nozzle 23 which drips thediffusing material 200 is disposed above the central portion WC of thesubstrate W in the vertical direction, the diffusing material 200 can beprecisely dripped onto the central portion WC of the substrate W, ascompared to the case where the first nozzle 23 is disposed in aninclined state like the second nozzle 26. Therefore, by dripping only asmall amount (e.g., about 1.5 ml) of the diffusing material 200, thediffusing material 200 can be wet-spread over the entire face of thesubstrate W. Further, in the present embodiment, by virtue of thepre-wet composition 210 being applied over the entire face of thesubstrate W thereby increasing the wettability, the diffusing agent 200is wet-spread over the entire face of the substrate Win a short time.Hence, in the present embodiment, the diffusing material 200 can beprecisely applied to the substrate W with a short tact.

After lifting up the nozzle part 21 to a predetermined height, as shownin FIG. 13F, the control part 9 controls the nozzle part 21 to bewithdrawn from the position facing the chuck part 20 to the standbyposition (nozzle withdrawing step S7). When the nozzle part 21 iswithdrawn from the chuck part 20, the chuck part 20 is rotated at arotation number of 2,000 rpm. The first nozzle 23 and the second nozzle26 are accommodated in the accommodation part 24 which is constituted bythe lid part 24 a contacting the main body 24 b at the standby position(see FIG. 11).

In the present embodiment, it is preferable that the chuck part 20, forexample, is accelerated from a rotation number of 800 rpm to a rotationnumber of 2,000 rpm φ within 1.0 seconds, and decelerated from arotation number of 2,000 rpm to a rotation number of 0 rpm within 0.5seconds at the time of stopping the rotating operation. In this manner,the entire tact required for the coating treatment of the diffusingmaterial 200 on the substrate W can be suppressed to 15 to 18 seconds.

Further, the coating film of the diffusing agent formed on the substrateW can be rendered to become a semi-dried state.

In the apparatus according to the present embodiment, simultaneouslywith the rotation of the chuck part 20, a back rinse treatment isconducted in which an alcohol as a cleaning liquid is ejected from theback face cleaning nozzle 22 a to the back face of the substrate W. Theejection of the cleaning liquid is started within 3 seconds fromstarting the rotation of the chuck part 20.

According to the apparatus of the present embodiment, as described abovewith reference to FIG. 10A and FIG. 10B, since the back face cleaningnozzle 22 a is disposed within 10 mm from the outer edge of thesubstrate W, the cleaning liquid supplied to the back face of thesubstrate W can be satisfactorily spread to the outer edge of thesubstrate W. By such configuration, the diffusing material 200 can beprevented from sneaking to the back face of the substrate W, and thereis no need to separately conduct a back rinse treatment after thecoating step. As a result, the tact of the coating step can be greatlyshortened.

After finishing the rotating operation, the chuck part 20 is lifted upto be withdrawn from the cup part 22. Thereafter, the control part 9actuates the substrate supporting member 62 of the first transportingapparatus 6, so as to receive the substrate W from the chuck part 20 andtransport the substrate W into the drying apparatus 3. Then, thediffusing material 200 on the substrate W is dried.

In the present embodiment, after unloading the substrate W having thediffusing material 200 coated thereon from the chuck part 20, thecontrol part 9 passes another substrate W from the loading part 1 to thecoating apparatus 10. At this time, the control part 9 mounts thesubstrate W on the chuck part 20 using another substrate supportingmember 62 of the first transporting apparatus 6. Then, while loading thesubstrate W having been coated with the diffusing material 200 into thedrying apparatus 3, the diffusing material 200 is applied to thesubstrate W inside the coating apparatus 10.

Subsequently, the control part 9 loads the substrate W into the dryingapparatus 3. The drying apparatus 3 conducts a drying treatment for eachsubstrate W at 150° C. for 10 seconds using hot plates 3 a, 3 b and 3 c.Based on such configuration, the substrate processing apparatus 100 iscapable of loading a substrate W into the drying apparatus 3 every 10seconds. By sequentially transporting the substrate W unloaded from thecoating apparatus 10 into the drying apparatus 3, the process speed canbe greatly improved.

Specifically, the substrate processing apparatus 100 mounts thesubstrate W which has been coated with the diffusing material 200 on thehot plate 3 a positioned most upstream. The hot plate 3 a dries thesubstrate W at 150° C. for 10 seconds. Then, the control part 9compresses the cylinder unit 54, and lifts down the substrate supportingmember 52 such that the upper end of thereof is lower than the upperface of the hot plate 3 a, so as to transfer the substrate W to the hotplate 3 b on the downstream side. The hot plate 3 b dries the substrateW at 150° C. for 10 seconds. Then, the control part 9 compresses thecylinder unit 54, and lifts down the substrate supporting member 52 suchthat the upper end of thereof is lower than the upper face of the hotplate 3 b, so as to transfer the dried substrate W to the hot plate 3 con the downstream side. The hot plate 3 c dries the substrate W at 150°C. for 10 seconds. In this manner, the substrate W can be subjected to adrying treatment at 150° C. for 30 seconds.

Alternatively, the heating temperatures of the hot plates 3 a, 3 b and 3c may be differentiated. For example, the hot plate 3 a may heat thesubstrate W at 60° C. for 10 seconds, the hot plate 3 b may heat thesubstrate W at 120° C. for 10 seconds, and the hot plate 3 c may heatthe substrate W at 150° C. for 10 seconds, so as to dry the substrate W.

In the present embodiment, the substrate W is transferred from the hotplate 3 a to the hot plate 3 b, and at the same time, the substratesupporting member 62 if the first transporting member 6 mounts thesubstrate W unloaded from coating apparatus 10 on the hot plate 3 a.Further, one substrate W is transferred from the hot plate 3 b to thehot plate 3 c, and at the same time, an unloading arm (not shown)unloads another substrate W on the hot plate 3 c from the substrateprocessing apparatus 100.

Thus, in the present embodiment, each substrate W is sequentiallytransferred to the hot plates 3 a, 3 b and 3 c, so as to conduct a heattreatment of the diffusing material 200. In this manner, a diffusingfilm can be formed on the surface of the substrate W.

By working the method of producing a solar cell according to the presentembodiment by a coating apparatus 10 as described above, since thenozzle part 21 of the coating apparatus 10 is equipped with a secondnozzle 26 capable of dripping the pre-wet composition 210 from adiagonally upper side of the central portion WC of the substrate W tothe central portion WC of the substrate W, after transferring the nozzlepart 21 above the substrate W, the pre-wet composition 210 and thediffusing material 200 can be dripped onto the substrate W withoutmoving the positions of the first nozzle 23 and the second nozzle 26. Assuch, since the transfer time of the nozzles 23 and 26 for dripping thematerials 200 and 210 onto the substrate W can be eliminated, the tactrequired for the coating treatment of the diffusing material 200 on thesubstrate W can be shortened.

Further, in the nozzle lift-down step S3, a configuration is employed inwhich the chuck part 20 having the substrate W mounted thereon istransferred from the substrate mounting position to the rotatingposition where the rotating operation is conducted in the cup part 22,and the nozzle part 21 is lifted down. As a result, dripping of thepre-wet composition 210 can be started at the timing when the chuck part20 reaches the rotating position, and the tact for the coating treatmentcan be shortened. Furthermore, a configuration is employed in which thenozzle lift-up step S6 is conducted before finishing the rotatingoperation of the chuck part 20. As a result, when the rotating operationof the chuck part 20 is finished, the nozzle part 21 is not disposedabove the chuck part 20, and by increasing the speed of lifting up thechuck part 20, the tact for the coating treatment can be shortened.Moreover, by controlling at the timing of the pre-wet compositiondripping step S4 and the diffusing material dripping step S5, a coatingapparatus 10 having a conventional configuration may be employed. As aresult, the cost of the substrate processing apparatus 100 can bereduced.

The method of producing a solar cell according to the present embodimentis not limited to the above apparatus configuration, and is workablewith other apparatuses.

In the present embodiment, example was given with respect to a casewhere the second nozzle 26 is held by the lid part 24 a such that theaxis which runs through the center of the opening 26 a is inclinedrelative to the vertical direction (Z direction). However, the firstnozzle 23 may be held by the lid part 24 a in an inclined state, as longas the diffusing material 200 can be satisfactorily dripped onto thecentral portion WC of the substrate W. Alternatively, each of the firstnozzle 23 and the second nozzle 26 may be held by the lid part 24 a inan inclined state.

Further, in the present embodiment, example was given with respect to acase where the lid part 24 a constitutes a regulation means whichregulates the landing position of the droplets of the pre-wetcomposition 210 such that the droplets are dripped on the centralportion WC of the substrate W. However, the present embodiment is notlimited thereto.

For example, as shown in FIG. 14, an adjustment apparatus 150 whichadjust the trajectory if the droplets by applying a physical externalforce may constitute a regulation means which regulates the landingposition of the droplets of the pre-wet composition such that thedroplets are dripped on the central portion of the substrate W. Suchadjustment apparatus 150 may be constituted of, for example, an airjetting apparatus, a magnetic force generating apparatus or the like. Inan adjustment apparatus 150 constituted of an air jetting apparatus, byadjusting the amount of air jetted, the trajectory of the droplets of atleast one of the materials 200 and 210 dripped from the first nozzle 23and the second nozzle 26 is adjusted, and the droplets can be landed onthe central portion WC of the substrate W. In an adjustment apparatus150 constituted of a magnetic force generating apparatus, by adjustingthe amount of magnetic force generated, the trajectory of the dropletsof at least one of the materials 200 and 210 dripped from the firstnozzle 23 and the second nozzle 26 is adjusted by the magnetic force,and the droplets can be landed on the central portion WC of thesubstrate W.

According to the method of producing a solar cell as described above,the amount of the diffusing agent used can be suppressed, and alsoformation defect of the coating film of the diffusing agent can besuppressed while shortening the tact time.

In the present embodiment, a textured structure is formed on the face Waof the substrate W. However, the present embodiment is not limitedthereto. Even if the face Wa does not have a textured structure, bypre-wetting with the pre-wet composition 210, formation defect of thecoating film of the diffusing agent can be suppressed.

Furthermore, in the present embodiment, explanation was given about acase where a textured structure is formed on the face Wa of thesubstrate W, and a monofacial power generation solar cell in which theface Wa is used as a light receiving face is produced. However, theproduction method of the present invention is also applicable to theproduction of a bifacial power generation solar cell which uses bothfaces of the substrate as light receiving faces. In the case of abifacial power generation solar cell, it is preferable to form atextured structure not only on the face Wa of the substrate W, but alsoon the other face. By virtue of forming a textured structure also on theother face, the utilization efficiency of the solar ray entering theother face, and a solar cell capable of generating power with highefficiency can be obtained.

Hereabove, examples of the preferred embodiments of the presentinvention has been described with the accompanying drawings, it shouldbe understood that these are exemplary of the invention and are not tobe considered as limiting. The form and combinations of the componentsshown in the aforementioned embodiment is only one example, and can bemodified depending on the design requirements without departing from thespirit or scope of the present invention.

For example, in the above embodiment, explanation was given takingexample of a method of producing a solar cell using a n-type substrate,and, hence, a boron compound (a compound of a group 13 element) is usedas the diffusing agent. However, the present invention is alsoapplicable to a method of producing a solar cell using a p-typesubstrate. In such a case, a diffusing material using the aforementionedcompound containing a group 15 element is prepared, and the surface ofthe substrate is pre-wetted, followed by spin-coating the diffusingmaterial, thereby forming a preferable coating film of the diffusingagent. Further, the present invention is also applicable to the casewhere a compound containing a group 15 element is applied to a face (oneface) of a p-type substrate, and a boron diffusing material is appliedto the face on the other side (other face).

As the p-type substrate, not only a monocrystalline silicon produced bythe aforementioned CZ process (Czochralski process), the FZ process(Floating Zone process) or the like, but also a multi crystallinesilicon may be used.

Example

As follows is a description of examples of the present invention,although the scope of the present invention is by no way limited bythese examples.

Example

One face of a n-type monocrystalline silicon substrate (diagonal length:200 mm, edge (linear portion): 156 mm, thickness: 180 μm) was subjectedto anisotropic etching using an alkali solution, so as to form atextured structure on the one face.

Subsequently, on the face having the textured structure formed, 1.0 g ofa PGME:DIW=1:1 mixed solvent was supplied, and the mixed solvent wasapplied to the face by spin-coating. Without stopping the rotation ofthe substrate, 0.5 g of a diffusing material was supplied on the facehaving the textured structure formed, and the diffusing material wasapplied to the face by spin-coating.

As the diffusing material, a boron diffusing material containing a borondiffusing agent and PGME as a solvent (EPLUS (registered trademark),SC-1008, manufactured by Tokyo Ohka) was used.

Further, referring to FIG. 6A, the spin-coating conditions were set asR1=800 rpm, R2=3,000 rpm, T1-T2=5 seconds, T2-T3=1 second, and T4-T5=5seconds.

After forming the coating film of the diffusing agent, the substrate wassequentially heated and dried at 60° C. for 10 seconds, 120° C. for 10seconds and 150° C. for 10 seconds, followed by heating in a nitrogenatmosphere at 1,000° C. for 30 minutes, so as to form a p⁺ impuritydiffusion layer. Although the heating was conducted in a nitrogenatmosphere, since a trace amount of oxygen was present, an oxide filmwas formed on the surface of the substrate.

Subsequently, the substrate was disposed inside a chamber. After purgingthe inside of the chamber with nitrogen to obtain a nitrogen atmosphere,POCl₃ was supplied into the chamber, followed by heating at 900° C. for15 minutes, so as to form a n⁺ impurity diffusion layer. In this manner,a solar cell substrate of Example was produced. 150 solar cellsubstrates were produced.

Comparative Example

The solar cell substrate of Comparative Example was produced in the samemanner as in Example, except that pre-wetting was not conducted.

On each of the solar cell substrates of Example and Comparative Example,an anti-reflection film made of silicon nitride was formed, followed byapplying a silver electrode on both faces of the solar cell substrate,so as to obtain a solar cell.

With respect to the obtained solar cells, the conversion efficiency(unit: %) and the reverse current (unit: A) were measured in accordancewith IEC 60904-3: 2008. The measurement conditions were temperature: 25°C., AM (air mass): 1.5G, and irradiation intensity: 1 kW/m². From thelight source, a continuous light was irradiated.

Further, in the measurement of the reverse current, the measurementvoltage was −12V.

FIG. 15A and FIG. 15 b are graphs showing the measurement results. FIG.15A shows the conversion efficiency, and FIG. 15B shows the amount ofreverse current. In each graph, the error bar is based on themeasurement results of n=150.

From the results of the measurements, it was found that, the conversionefficiency was at about the same level in Example and ComparativeExample, but the reverse current was more suppressed in Example than inComparative Example. It is presumed that, in Example, a coating film ofthe diffusing agent was satisfactorily formed, and reverse current wassuppressed.

From the results shown above, it was found that the present invention isuseful.

DESCRIPTION OF REFERENCE CHARACTERS AND NUMERALS

200: diffusing material, 210: pre-wet composition, 1002: p⁺Si layer(first impurity diffusion layer), 1004: n⁺Si layer (second impuritydiffusion layer), T: textured structure, W: substrate, Wa: one face

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions, and other modifications can be made withoutdeparting from the spirit or scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description, and is only limited by the scope of theappended claims.

What is claimed is:
 1. A method of producing a solar cell, comprising: afirst coating step in which a pre-wet composition is spin-coated on oneface of a semiconductor substrate; a second coating step in which adiffusing material including a solvent and a diffusing agent containinga first impurity element is spin-coated on the one face where thepre-wet composition has been spin-coated, so as to form a coating filmof the diffusing agent; and a first impurity diffusion layer formingstep in which the semiconductor substrate having the coating film formedthereon is heated, so as to form a first impurity diffusion layer inwhich the first impurity element contained in the diffusing agent isdiffused, wherein: from the start of the first coating step to the endof the second coating step, spin-coating is continuously conductedwithout stopping rotating the semiconductor substrate, a maximumsubstrate rotation number R2 in the second coating step is larger than amaximum substrate rotation number R1 in the first coating step, in thesecond coating step, after supplying the diffusing material to the oneface, the substrate rotation number in the first coating step isincreased to the substrate rotation number in the second coating step,the maximum substrate rotation number R1 in the first coating step is inthe range of 800 rpm to 3,000 rpm, and the maximum substrate rotationnumber R2 in the second coating step is in the range of 1,000 rpm to5,000 rpm, the rotation speed of the semiconductor substrate isaccelerated from 0 rpm to the maximum substrate rotation number R1 fromthe start of the rotation to a time T1 just before applying the pre-wetcomposition to the semiconductor substrate, and the rotation time of thesemiconductor substrate from the start of the rotation to the time T1 is0.01 to 0.2 seconds, the rotation speed of the semiconductor substrateis maintained at the maximum substrate rotation number R1 from the timeT1 to a time T2 when the spin-coating of the pre-wet composition isfinished and just before applying the diffusing material to thesemiconductor substrate, and the rotation time of the semiconductorsubstrate from the time T1 to the time T2 is 0.5 to 5 seconds, therotation speed of the semiconductor substrate is maintained at themaximum substrate rotation number R1 from the time T2 to a time T3 whenthe rotation speed of the semiconductor substrate is started to beaccelerated, and the rotation time of the semiconductor substrate fromthe time T2 to the time T3 is 0.5 to 1 second, the rotation speed of thesemiconductor substrate is accelerated from the time T3 to a time T4when the rotation speed of the semiconductor substrate reaches themaximum substrate rotation number R2, and the rotation time of thesemiconductor substrate from the time T3 to the time T4 is 0.1 to 1second, the rotation speed of the semiconductor substrate is maintainedat the maximum substrate rotation number R2 from the time T4 to the timeT5 when the spin-coating of the diffusing material is finished, and therotation time of the semiconductor substrate from the time T4 to thetime T5 is 3 to 8 seconds, and the rotation speed of the semiconductorsubstrate is reduced from the maximum substrate rotation number R2 to 0rpm from the time T5 to a time T6 when the second coating step isfinished, and the rotation time of the semiconductor substrate from thetime T5 to the time T6 is 0.1 to 1 second.
 2. The method according toclaim 1, which comprises, prior to the first coating step, a step inwhich a textured structure is formed on at least the one face.
 3. Themethod according to claim 1, wherein the second coating step comprisesforming the coating film in a semi-dried state.
 4. The method accordingto claim 1, which comprises, after the first impurity diffusion layerforming step, a second impurity diffusion layer formed step in which asecond impurity diffusion layer having a second impurity elementdiffused therein is formed on a second face of the semiconductorsubstrate, the second face being opposite the first face.